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Am J Physiol Endocrinol Metab. 2004 Jan;286(1):E77-84. Epub 2003 Sep 16.

Distributed control of glucose uptake by working muscles of conscious mice: roles of transport and phosphorylation.

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1
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-0615, USA. patrick.fueger@vanderbilt.edu

Abstract

Muscle glucose uptake (MGU) is determined by glucose delivery, transport, and phosphorylation. C57Bl/6J mice overexpressing GLUT4, hexokinase II (HK II), or both were used to determine the barriers to MGU. A carotid artery and jugular vein were catheterized for arterial blood sampling and venous infusions. Experiments were conducted in conscious mice approximately 7 days after surgery. 2-Deoxy-[3H]glucose was administered during rest or treadmill exercise to calculate glucose concentration-dependent (Rg) and -independent (Kg) indexes of MGU. Compared with wild-type controls, GLUT4-overexpressing mice had lowered fasting glycemia (165 +/- 6 vs. 115 +/- 6 mg/dl) and increased Rg by 230 and 166% in the gastrocnemius and superficial vastus lateralis (SVL) muscles under sedentary conditions. GLUT4 overexpression was not able to augment exercise-stimulated Rg or Kg. Whereas HK II overexpression had no effect on fasting glycemia (170 +/- 6 mg/dl) or sedentary Rg, it increased exercise-stimulated Rg by 82, 60, and 169% in soleus, gastrocnemius, and SVL muscles, respectively. Combined GLUT4 and HK II overexpression lowered fasting glycemia (106 +/- 6 mg/dl), increased nonesterified fatty acids, and increased sedentary Rg. Combined GLUT4 and HK II overexpression did not enhance exercise-stimulated Rg compared with HK II-overexpressing mice because of the reduced glucose concentration. GLUT4 combined with HK II overexpression resulted in a marked increase in exercise-stimulated Kg. In conclusion, control of MGU shifts from membrane transport at rest to phosphorylation during exercise. Glucose transport is not normally a significant barrier during exercise. However, when the phosphorylation barrier is lowered by HK II overexpression, glucose transport becomes a key site of control for regulating MGU during exercise.

PMID:
13129858
DOI:
10.1152/ajpendo.00309.2003
[Indexed for MEDLINE]
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